In many areas of process and power engineering that are of relevance to safety the trouble-free operation of a system depends on the smooth functioning of the machines or machine parts employed. In order to avoid costly, erratic interruptions to operation, any damage to valves or bearings, for instance, should as far as possible be detected at the initial stage, which is to say before a component outage can bring the system to a halt. As an instance of this, defective valve seats will result in leakage flows that produce broadband ultrasonic emissions. Picking up and evaluating the ultrasonic emissions of a valve can hence serve to detect valve damage early. An ultrasonic pick-up suitable for picking up the solid-borne sound signal is known from DE 299 12 847 U 1. Said pick-up has a housing containing a piezoelectric measuring element and a circuit for signal conditioning. The conditioned measurement signal can be ducted as an output signal over a cable to a remotely located evaluation device. The auxiliary power required to operate the signal conditioning circuit is supplied by the evaluation device and made available to the acoustic pick-up likewise via the cable. This means an additional device for generating the auxiliary power is required in the evaluation device and additional wires for transmitting said auxiliary power are required in the cable.
A monitoring sensor using wireless signal transmission (wireless transducer) is known from EP 1 022 702 A2, which wireless transducer has, mounted within a housing, a piezoelectric sensing element for generating an electric monitoring signal and an electronic circuit.
The auxiliary energy required to operate the electronic circuit and for signal transmission is obtained from the electric monitoring signal.
A further monitoring system using wireless signal transmission is known from U.S. Pat. No. 4,237,454.